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Old 16th February 2012, 12:21 AM   #1131
rsdio is offline rsdio  United States
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Quote:
Originally Posted by linuxworks View Post
I picked 24bit i2s which I thought would be correct. if 16bits comes in, 24 bits are still sent (?) but just padded with zero, right?

if things were shifted even 1 bit, I'd hear overflows on everything, wouldn't I? ie, half volume would be max volume and every single cd today has averages well over half-scale sample values.
Half-scale is only 6 dB down, and sounds a lot louder than half volume, due to the logarithmic nature of human hearing. But you're right, you'd probably hear overflows on just about everything.

Last edited by rsdio; 16th February 2012 at 12:27 AM.
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Old 16th February 2012, 12:25 AM   #1132
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this has nothing to do with the usb i2s stuff; its a pcm5102 problem.
I was going to say that the DAC chip isn't really 100% responsible for what you hear. A common problem is that the analog section between the DAC output and the RCA jack can be overloaded.

However, I took a quick look at the PCM5102 data sheet, and I see that their recommended circuit is nothing but a resistor and capacitor. It's really difficult to clip passive parts (other than inductors), so the problem seems to be the responsibility of the PCM5102, as you said. Personally, I think this makes the PCM5100 series look like a really bad choice for audiophile.
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Old 16th February 2012, 01:23 AM   #1133
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I just checked and the AK4103 with the cable drive capability is available from Digikey. The single piece price is a little higher than I would like to see knowing the 10K pricing but its not a big issue at $4.71.
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Old 16th February 2012, 01:25 AM   #1134
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Demian, that's a 5V part if I'm right. To me that means running it off VBUS since we haven't really established a design for external power.

The CS8604 is 3.3V. Are there serious reasons, not just gut feeling as to why it should be replaced?

Børge
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Old 16th February 2012, 03:04 AM   #1135
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VBus would be fine. Its a dedicated DIT that supports all of the standards. I believe it can be hard programmed so no CPU requirements. It can drive SPDIF or AES/EBU directly. If its not sharing power with any sensitive circuitry then it won't affect them. The AES/EBU drive requires 5V (8V P-P output, the real reason AES can sound better than SPDIF, more signal to noise).
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Old 16th February 2012, 06:30 AM   #1136
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ha! I had one of those chips, too, in my parts bin. not even opened and still in its mouser pkg.

soldered one up:

Click the image to open in full size.

and I'll connect it to the audio widget's i2s tomorrow and see how it flies.

the lead pitch was MUCH easier to deal with than the wolfson. its a larger part but I prefer easier-to-solder over smaller size.

I'll connect her tomorrow and see if bits come out
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Old 16th February 2012, 01:04 PM   #1137
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VBus would be fine. Its a dedicated DIT that supports all of the standards. [...] If its not sharing power with any sensitive circuitry then it won't affect them. The AES/EBU drive requires 5V (8V P-P output, the real reason AES can sound better than SPDIF, more signal to noise).
It is not possible to run a 5 V chip directly from Vbus. That's because nearly all 5 V chips have an absolute minimum voltage requirement of 4.75 V, but Vbus can legally drop to 4.35 V or even 4.01 V in certain situations such as when attached to an unpowered hub.

What is needed is a boost regulator. Inductive boosts can create noise, but Maxim has parts like the MAX1595 that only need capacitors and thus run quieter.

Of course, if you want external power for isolation reasons, then 5 V is no problem, or even 18 V.
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Old 16th February 2012, 03:58 PM   #1138
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From the spec:
Quote:
Functions drawing more than one unit load must operate with a 4.75 V minimum input voltage at the
connector end of their upstream cables.
The AB1.1 draws more than 2 unit loads. If this were a USB product headed for certification these would be valid issues to address but a DIY audiophile device can be expected to have more stringent power requirements than the worst case USB spec. Eliminating a regulator actually reduces parts count.

Also, while the output can't be guaranteed to meet the Vout high spec its unlikely that the chip will stop functioning at 4.74V or even much lower since its all digital. The prop delays may change and it would not have the full AES drive at 4V but I would not be surprised to see a decent signal at the far end of a cable. Just don't do this if you are planning to make 10,000 units.
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Old 16th February 2012, 07:43 PM   #1139
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I'm looking at the 8406 schematic you recently posted, now.

you are going to talk to that chip in software mode? it seems so (?)

you have a circle labeled 'spdif' on pin4/rxp. that will set the serial input format I think? is there a reason to not just set this chip to i2s mode?

I'm going to try to config and test the chip in hw mode since I consider this a pretty 'dumb' function and I'd rather not have to chat with the chip if I don't have to
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Old 17th February 2012, 12:07 AM   #1140
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Hi guys,

I'm not going to put in a boost converter for the digital output! There are plenty 3.3V parts out there which will run from the same LDO as powers the DAC today.

Quoting page 38 of the CS8406 data sheet: "The AES3 and IEC60958-4 specifications call for a balanced output drive of 2-7V peak-to-peak into a 110 Ω ±20% load with no cable attached."

So 3.3V supply shouldn't be an issue.

I have set it ut in SW mode because that is more flexible and because there is an available I2C bus. I agree that it would be easy to set it up for straightforward I2S. The only thing is table 4 on page 29 to set the sampling frequency relative to MCLK. That looks to me like two GPIO pins coming from the MCU, so - I thought - it might be just as good to configure the whole thing in firmware.

The SPDIF pin on the MCU doesn't really do anything. But for the future I want to be able to use a module which has a CMOS-level SPDIF line. So this is only about reserving a GPIO line for future use.

Børge

Quote:
Originally Posted by linuxworks View Post
I'm looking at the 8406 schematic you recently posted, now.

you are going to talk to that chip in software mode? it seems so (?)

you have a circle labeled 'spdif' on pin4/rxp. that will set the serial input format I think? is there a reason to not just set this chip to i2s mode?

I'm going to try to config and test the chip in hw mode since I consider this a pretty 'dumb' function and I'd rather not have to chat with the chip if I don't have to
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